This invention relates to a channel selector for use in television receivers, FM (frequency modulation) radio receivers, AM (amplitude modulation) radio receivers and so on.
FIG. 1 is a block diagram of a conventional channel selector using a PLL (phase-locked loop) frequency synthesizer. The PLL frequency synthesizer has a loop consisting of a voltage controlled local oscillator 1, a prescaler 2, a programmable frequency divider 3, a phase comparator 4 and a low pass filter 5 and has a configuration such that an output of a reference oscillator 6 is divided by a reference frequency divider 7 and applied to an input terminal of the phase comparator 4, and an output code of a code converter 9 controlled by a channel entry apparatus 8 determines the frequency dividing ratio of the programmable frequency divider 3, the output of which is applied to the other input terminal of the phase comparator 4. The local oscillating frequency of a desired receiving channel is synthesized by the PLL frequency synthesizer mentioned above. The local oscillation output and the output of a radio frequency amplifier 10 are mixed in a mixer 11 so as to obtain an intermediate frequency output. This output is amplified in an intermediate frequency amplifier 12 and detected in a detector 13. The detected signal is conveyed through an output circuit 14 and applied to an output apparatus 15. A channel number indicator 16 indicates which channel is received.
Recently, home-video-tape recorders (VTR) have been widely used. Using such VTR, a record-desired program which is simultaneously received with the other on-screen program can be recorded. And recently, sound-multiplex in television broadcast started in Japan. Because the sound became stereophonic, a tuner unit which incorporates television-channel selector, FM and AM radio-channel selector is desired to be developed. Further in future, development of the independent use of the sound multiplex broadcast such as facsimile is expected. In such cases, a plurality of receivers is necessary, and if a channel selector is provided with each of said receivers, a plurality of channel selectors are necessary, but this is not undesirable from the view point of cost.